Proposed FDA reference grass extracts of Bermuda, june, orchard, perennial rye, sweet vernal, and timothy were evaluated for stability when diluted with HSA-saline diluent and stored continuously at 2-8~C for up to 1 year. The dilution factor for each grass ranged from 1: 1.5 millionth to 1:22.5 millionth. Relative potency of the stored extract was determined with respect to a freshly reconstituted reference using parallel line skin test assay. All grass extracts were equipotent to a freshly reconstituted reference for up to 1 year except for timothy which was equipotent to its reference for up to 3 months, but fell below the 95% lower limit of potency at 1 year. These data indicate that highly diluted standardized grass extracts remain stable for months when diluted with HSA diluent and stored continuously at 2- 8 C. Additional stability data using subjects reactive to heat labile grass allergens are proposed.